Distributed process control systems, like those used in chemical, petroleum, or other process plants, typically include one or more process controllers communicatively coupled to one or more field devices via analog, digital, or combined analog/digital buses, or via a wireless communication link or network. The field devices, which may be, for example, valves, valve positioners, switches, and transmitters (e.g., temperature, pressure, level and flow rate sensors), are located within the process environment and generally perform physical or process control functions, such as opening or closing valves, or measuring process parameters to control one or more processes executing within the process plant or system. The process controllers, which are also typically located within the plant environment, may be configured to receive signals indicative of process measurements made by sensors or field devices, as well as other information pertaining to the field devices. The process controllers further execute controller applications that run, for example, different control modules that make process control decisions, generate control signals based on the received information, and coordinate with the control modules or blocks being performed in the field devices, such as HART®, Wireless HART®, and FOUNDATION® Fieldbus field devices. The control modules in the controller send the control signals over the communication lines or links to the field devices to thereby control the operation of at least a portion of the process plant or system.
Field devices may be either single-variable devices or may be multi-variable devices, such as smart field devices. Single-variable devices generate only one output variable value, while multi-variable devices generate a plurality of values corresponding out a plurality of output variables. Multi-variable devices include field devices measuring a plurality of process variables associated with conditions within a process plant, as well as other devices generating output data for a plurality of output variables. Multi-variable devices include smart field devices, such as field devices conforming to the well-known Fieldbus protocol may also perform control calculations, alarming functions, and other control functions commonly implemented within a controller. Field devices within a process control system are represented by device objects, which each device object includes a primary parameter for the primary output variable of the field device. A device object representing a multi-variable field device also includes one or more subsequent parameters (e.g., secondary or tertiary parameters) associated with additional output variables of the multi-variable field device, in addition to a primary parameter associated with the primary output variable.
Information from the field devices and the controller is usually made available over a data highway to one or more other hardware devices, such as operator workstations, personal computers, or computing devices, data historians, report generators, centralized databases, or other centralized administrative computing devices that are typically placed in control rooms or other locations away from the harsher plant environment. Each of these hardware devices typically is centralized across the process plant or across a portion of the process plant. These hardware devices run applications that may, for example, enable an operator to perform functions with respect to controlling a process or operating the process plant, such as changing settings of the process control routine, modifying the operation of the control modules within the controllers or the field devices, viewing the current state of the process, viewing alarms generated by field devices and controllers, simulating the operation of the process for the purpose of training personnel or testing the process control software, keeping and updating a configuration database, etc. The data highway utilized by the hardware devices, controllers, and field devices may include a wired communication path, a wireless communication path, or a combination of wired and wireless communication paths.
As an example, the DeltaV™ control system, sold by Emerson Process Management, includes multiple applications stored within and executed by different devices located at diverse places within a process plant. Each of these applications provides a user-interface (UI) to allow a user (e.g., a configuration engineer, a process plant operator, a maintenance technician, etc.) to view or modify aspects of the process plant operation and configuration. Throughout this specification, the phrase “user interface” or “UI” is used to refer to an application or screen that allows a user to view or modify the configuration, operation, or status of the process plant. Similarly, the phrase “user-interface device” or “UI device” is used to refer to a device on which a user interface is operating, whether that device is stationary (e.g., a workstation, wall-mounted display, process control device display, etc.) or mobile (e.g., a laptop computer, tablet computer, smartphone, etc.). A configuration application, which resides in one or more operator workstations or computing devices, enables users to create or change process control modules and download these process control modules via a data highway to dedicated distributed controllers. Typically, these control modules are made up of communicatively interconnected function blocks. The configuration application may also allow a configuration designer to create or change operator interfaces which are used by a viewing application to display data to an operator and to enable the operator to change settings, such as set points, within the process control routines. Each dedicated controller and, in some cases, one or more field devices, stores and executes a respective controller application that runs the control modules assigned and downloaded thereto to implement actual process control functionality. The viewing applications, which may be executed on one or more operator workstations (or on one or more remote computing devices in communicative connection with the operator workstations and the data highway), receive data from the controller application via the data highway and display this data to process control system designers, operators, or users using the UIs, and may provide any of a number of different views, such as an operator's view, an engineer's view, a technician's view, etc. A data historian application is typically stored in and executed by a data historian device that collects and stores some or all of the data provided across the data highway while a configuration database application may run in a still further computer attached to the data highway to store the current process control routine configuration and data associated therewith. Alternatively, the configuration database may be located in the same workstation as the configuration application.
In existing process control systems, control of the process plant involves the operation of one or more control modules implementing process control logic that communicate with field devices to send and receive process control data. Because the field devices may use any of various operation and communication protocols, the control modules must be configured to accept and provide the process control data using the appropriate protocols for each device. In addition, communication links between the control modules and the field devices may add further layers of communication protocols or formats for proper transmission and receipt of process control data. Thus, process control systems typically include a large number of field devices and control modules that receive data generated by the field devices. To simplify configuration and operation of process control systems, field device tags may be used to identify the field devices by a unique name within the process control system. Once configured, the device tag may be used to refer to the field device without requiring specification of the full path within the system to the field device. Although such tags are useful for single-variable field devices, problems arise when such tags are applied to multi-variable devices. Within existing control systems, subsequent parameters of multi-variable field device objects cannot be readily identified using tags or other simplified references, due to limitations in the communication protocols utilized. The invention described herein addresses these issues.